The invention relates to an AM detector circuit. More particularly, the invention relates to a synchronous detector circuit having an AGC function or capability.
It is essential for an AM detector circuit to be provided with an AGC (automatic gain control) circuit. An AGC circuit in which the output level of an AM detector circuit is detected and the gain of an amplifier controlled according to the output level thus detected and an AGC circuit utilizing a current division technique and employing a differential amplifier have been extensively employed for such AM detector circuits. In both of the described prior art circuits, the dynamic range is limited. Accordingly, if the input signal to the circuit is large, the input level tends to saturate and therefore cause various types of distortion and increase the amount of spurious interference.
Accordingly, an object of the invention is to provide an AM detector circuit having an AGC function in which the above-described drawbacks accompanying a conventional AM detector circuit have been eliminated and very little signal distortion is caused.